A projection system includes a projector that projects an image onto a projection plane of a screen, and sensor units each including a photoelectric power generating unit that is installed at a predetermined position in an area in which an image is projected on the projection plane and that generates power corresponding to an intensity of projection light projected by the projector. The projector may include an image processing circuit that converts at least image data projected at the installation positions of the sensor units in image data projected on the projection plane into white image data or converts whole image data into white image data.